Method and apparatus for selecting mme in wireless communication system including mobile relay node

ABSTRACT

A method and apparatus for selecting a mobility management entity (MME) in a wireless communication system including a mobile relay node is provided. A donor eNodeB (DeNB) receives a mobile relay indicator from the mobile relay node during a radio resource control (RRC) connection establishment procedure, receives a mobile relay support indication from an MME supporting the mobile relay node during an S1 setup procedure between the MME and the DeNB, and selects the MME supporting the mobile relay node among a plurality of MMEs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisionalapplication No. 61/497,925 filed on Jun. 16, 2011, which is incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication system, and moreparticularly, to a method and apparatus for selecting a mobilitymanagement entity (MME) in a wireless communication system including amobile relay node.

2. Related Art

Universal mobile telecommunications system (UMTS) is a 3rd generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS). The E-UMTS may be also referred to asan LTE system. The communication network is widely deployed to provide avariety of communication services such as voice over internet protocol(VoIP) through IMS and packet data.

As illustrated in FIG. 1, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an evolved packet core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNB) 20, and a plurality of user equipment (UE) 10. Oneor more E-UTRAN mobility management entity (MME)/system architectureevolution (SAE) gateways 30 may be positioned at the end of the networkand connected to an external network.

As used herein, “downlink” refers to communication from eNB 20 to UE 10,and “uplink” refers to communication from the UE to an eNB. UE 10 refersto communication equipment carried by a user and may be also referred toas a mobile station (MS), a user terminal (UT), a subscriber station(SS) or a wireless device.

An eNB 20 provides end points of a user plane and a control plane to theUE 10. MME/SAE gateway 30 provides an end point of a session andmobility management function for UE 10. The eNB and MME/SAE gateway maybe connected via an S1 interface.

The eNB 20 is generally a fixed station that communicates with a UE 10,and may also be referred to as a base station (BS) or an access point.One eNB 20 may be deployed per cell. An interface for transmitting usertraffic or control traffic may be used between eNBs 20.

The MME provides various functions including NAS signaling to eNBs 20,NAS signaling security, AS security control, Inter CN node signaling formobility between 3GPP access networks, Idle mode UE reachability(including control and execution of paging retransmission), trackingarea list management (for UE in idle and active mode), PDN GW andserving GW selection, MME selection for handovers with MME change, SGSNselection for handovers to 2G or 3G 3GPP access networks, roaming,authentication, bearer management functions including dedicated bearerestablishment, support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingper-user based packet filtering (by e.g. deep packet inspection), lawfulinterception, UE IP address allocation, transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNB 20 and gateway 30 viathe S1 interface. The eNBs 20 may be connected to each other via an X2interface and neighboring eNBs may have a meshed network structure thathas the X2 interface.

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

As illustrated, eNB 20 may perform functions of selection for gateway30, routing toward the gateway during a radio resource control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of broadcast channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, system architecture evolution (SAE) bearercontrol, and ciphering and integrity protection of non-access stratum(NAS) signaling.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 3( a) is block diagram depicting the user-plane protocol, and FIG.3( b) is block diagram depicting the control-plane protocol. Asillustrated, the protocol layers may be divided into a first layer (L1),a second layer (L2) and a third layer (L3) based upon the three lowerlayers of an open system interconnection (OSI) standard model that iswell known in the art of communication systems.

The physical layer, the first layer (L1), provides an informationtransmission service to an upper layer by using a physical channel. Thephysical layer is connected with a medium access control (MAC) layerlocated at a higher level through a transport channel, and data betweenthe MAC layer and the physical layer is transferred via the transportchannel. Between different physical layers, namely, between physicallayers of a transmission side and a reception side, data is transferredvia the physical channel.

The MAC layer of Layer 2 (L2) provides services to a radio link control(RLC) layer (which is a higher layer) via a logical channel. The RLClayer of Layer 2 (L2) supports the transmission of data withreliability. It should be noted that the RLC layer illustrated in FIGS.3( a) and 3(b) is depicted because if the RLC functions are implementedin and performed by the MAC layer, the RLC layer itself is not required.The PDCP layer of Layer 2 (L2) performs a header compression functionthat reduces unnecessary control information such that data beingtransmitted by employing internet protocol (IP) packets, such as IPv4 orIPv6, can be efficiently sent over a radio (wireless) interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer located at the lowest portion ofthe third layer (L3) is only defined in the control plane and controlslogical channels, transport channels and the physical channels inrelation to the configuration, reconfiguration, and release of the radiobearers (RBs). Here, the RB signifies a service provided by the secondlayer (L2) for data transmission between the terminal and the UTRAN.

As illustrated in FIG. 3( a), the RLC and MAC layers (terminated in aneNB 20 on the network side) may perform functions such as scheduling,automatic repeat request (ARQ), and hybrid automatic repeat request(HARQ). The PDCP layer (terminated in eNB 20 on the network side) mayperform the user plane functions such as header compression, integrityprotection, and ciphering.

As illustrated in FIG. 3( b), the RLC and MAC layers (terminated in aneNodeB 20 on the network side) perform the same functions for thecontrol plane. As illustrated, the RRC layer (terminated in an eNB 20 onthe network side) may perform functions such as broadcasting, paging,RRC connection management, radio bearer (RB) control, mobilityfunctions, and UE measurement reporting and controlling. The NAS controlprotocol (terminated in the MME of gateway 30 on the network side) mayperform functions such as a SAE bearer management, authentication,LTE_IDLE mobility handling, paging origination in LTE_IDLE, and securitycontrol for the signaling between the gateway and UE 10.

The RRC state may be divided into two different states such as aRRC_IDLE and a RRC_CONNECTED. In RRC_IDLE state, the UE 10 may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform PLMN selection and cellre-selection. Also, in RRC_IDLE state, no RRC context is stored in theeNB.

In RRC_CONNECTED state, the UE 10 has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the network (eNB) becomes possible. Also, the UE 10 can reportchannel quality information and feedback information to the eNB.

In RRC_CONNECTED state, the E-UTRAN knows the cell to which the UE 10belongs. Therefore, the network can transmit and/or receive data to/fromUE 10, the network can control mobility (handover and inter-RAT cellchange order to GERAN with NACC) of the UE, and the network can performcell measurements for a neighboring cell.

In RRC_IDLE state, the UE 10 specifies the paging DRX cycle.Specifically, the UE 10 monitors a paging signal at a specific pagingoccasion of every UE specific paging DRX cycle.

The paging occasion is a time interval during which a paging signal istransmitted. The UE 10 has its own paging occasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE 10 moves from one tracking area to anothertracking area, the UE will send a tracking area update message to thenetwork to update its location.

FIG. 4 shows an example of structure of a physical channel.

The physical channel transfers signaling and data between layer L1 of aUE and eNB. As illustrated in FIG. 4, the physical channel transfers thesignaling and data with a radio resource, which consists of one or moresub-carriers in frequency and one more symbols in time.

One sub-frame, which is 1 ms in length, consists of several symbols. Theparticular symbol(s) of the sub-frame, such as the first symbol of thesub-frame, can be used for downlink control channel (PDCCH). PDCCHscarry dynamic allocated resources, such as PRBs and MCS.

A transport channel transfers signaling and data between the L1 and MAClayers. A physical channel is mapped to a transport channel.

Downlink transport channel types include a broadcast channel (BCH), adownlink shared channel (DL-SCH), a paging channel (PCH) and a multicastchannel (MCH). The BCH is used for transmitting system information. TheDL-SCH supports HARQ, dynamic link adaptation by varying the modulation,coding and transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The PCH is used for paging a UE. The MCH is usedfor multicast or broadcast service transmission.

Uplink transport channel types include an uplink shared channel (UL-SCH)and random access channel(s) (RACH). The UL-SCH supports HARQ anddynamic link adaptation by varying the transmit power and potentiallymodulation and coding. The UL-SCH also may enable the use ofbeamforming. The RACH is normally used for initial access to a cell.

The MAC sublayer provides data transfer services on logical channels. Aset of logical channel types is defined for different data transferservices offered by MAC. Each logical channel type is defined accordingto the type of information transferred.

Logical channels are generally classified into two groups. The twogroups are control channels for the transfer of control planeinformation and traffic channels for the transfer of user planeinformation.

Control channels are used for transfer of control plane informationonly. The control channels provided by MAC include a broadcast controlchannel (BCCH), a paging control channel (PCCH), a common controlchannel (CCCH), a multicast control channel (MCCH) and a dedicatedcontrol channel (DCCH). The BCCH is a downlink channel for broadcastingsystem control information. The PCCH is a downlink channel thattransfers paging information and is used when the network does not knowthe location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by MAC include a dedicated trafficchannel (DTCH) and a multicast traffic channel (MTCH). The DTCH is apoint-to-point channel, dedicated to one UE for the transfer of userinformation and can exist in both uplink and downlink. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude a DCCH that can be mapped to UL-SCH, a DTCH that can be mappedto UL-SCH and a CCCH that can be mapped to UL-SCH. Downlink connectionsbetween logical channels and transport channels include a BCCH that canbe mapped to BCH or DL-SCH, a PCCH that can be mapped to PCH, a DCCHthat can be mapped to DL-SCH, and a DTCH that can be mapped to DL-SCH, aMCCH that can be mapped to MCH, and a MTCH that can be mapped to MCH.

Meanwhile, 3GPP LTE-A may supports relaying by having a relay node (RN)wirelessly connect to an eNB serving the RN. It may be referred toParagraph 4.7 of “Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); and EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN); Overalldescription; Stage 2 (release 10)” to 3GPP (3rd generation partnershipproject) TS 36.300 V10.2.0 (2010-12). The eNB serving the RN may bereferred as donor eNB (DeNB). The DeNB and the RN may be connected via amodified version of the E-UTRA radio interface. The modified vision maybe referred as a Un interface.

The RN may support eNB functionality. It means that the RN terminatesthe radio protocols of the E-UTRA radio interface, and an S1 and X2interfaces. In addition to the eNB functionality, the RN may alsosupport a subset of UE functionality, e.g, a physical layer, layer-2,RRC, and NAS functionality, in order to wirelessly connect to the DeNB.

FIG. 5 shows a block diagram illustrating network structure of an LTE-Asystem introducing a relay system.

Referring to FIG. 5, the LTE-A network includes an E-UTRAN, an EPC andone or more user equipment (not described). The E-UTRAN may include oneor more eNB 111, one or more donor eNB (DeNB) 110, one or more relaynode (RN) 100 and a plurality of UE may be located in one cell. One ormore E-UTRAN MME/S-GW 120 may be positioned at the end of the networkand connected to an external network.

As used herein, “downlink” refers to communication from the eNB 111 tothe UE, from the DeNB 110 to the UE or from the RN 100 to the UE, and“uplink” refers to communication from the UE to the eNB 111, from the UEto the DeNB 110 or from the UE to the RN 100. The UE refers tocommunication equipment carried by a user and may be also referred to asa mobile station (MS), a user terminal (UT), a subscriber station (SS)or a wireless device.

The eNB 111 and the DeNB 110 provide end points of a user plane and acontrol plane to the UE. MME/S-GW 120 provides an end point of a sessionand mobility management function for UE. The eNB 111 and the MME/S-GW120 may be connected via an S1 interface. The DeNB 110 and MME/SAEgateway 120 may be connected via an S1 interface. The eNBs 111 may beconnected to each other via an X2 interface and neighboring eNBs mayhave a meshed network structure that has the X2 interface. The eNB 111and the DeNB 110 may be connected to each other via an X2 interface.

The RN 100 may be wireles sly connected to the DeNB 110 via a modifiedversion of the E-UTRA radio interface being called the Un interface.That is, the RN 100 may be served by the DeNB 110. The RN 100 maysupport the eNB functionality which means that it terminates the S1 andX2 interfaces. Functionality defined for the eNB 111 or the DeNB 110,e.g. radio network layer (RNL) and transport network layer (TNL), mayalso apply to RNs 100. In addition to the eNB functionality, the RN 100may also support a subset of the UE functionality, e.g. physical layer,layer-2, RRC, and NAS functionality, in order to wirelessly connect tothe DeNB.

The RN 100 may terminate the S1, X2 and Un interfaces. The DeNB 110 mayprovide S1 and X2 proxy functionality between the RN 100 and othernetwork nodes (other eNBs, MMEs and S-GWs). The S1 and X2 proxyfunctionality may include passing UE-dedicated S1 and X2 signalingmessages as well as GTP data packets between the S1 and X2 interfacesassociated with the RN 100 and the S1 and X2 interfaces associated withother network nodes. Due to the proxy functionality, the DeNB 110appears as an MME (for S1) and an eNB (for X2) to the RN.

The DeNB 110 may also embed and provides the S-GW/P-GW-like functionsneeded for the RN operation. This includes creating a session for the RN100 and managing EPS bearers for the RN 100, as well as terminating theS11 interface towards the MME serving the RN 100.

The RN and the DeNB may also perform mapping of signaling and datapackets onto EPS bearers that are setup for the RN. The mapping may bebased on existing QoS mechanisms defined for the UE and the P-GW.

The relay node may be classified to a fixed relay node and a mobilerelay node. The mobile relay node may be applied to the 3GPP LTE rel-11.One of the possible deployment scenarios of mobile relay node is highspeed public transportation, e.g, a high speed railway. That is, themobile relay node may be put on the top of a high speed train. Hence, itis easily expected that the provision of various good quality servicestowards the users on a high speed public transportation will beimportant. Meanwhile, the service requirements offered by the fixedrelay node seem to be different from those offered by the mobile relaynode. So, there might be a few of considerations that should be resolvedin the mobile relay node. The solutions to resolve these considerationsfor mobile relay node may have impacts on radio a radio access network(RAN).

A S1-flex concept provides support for network redundancy and loadsharing of traffic across network elements in a core network (CN), theMME and the S-GW, by creating pools of MMEs and S-GWs and allowing eacheNB to be connected to multiple MMEs and S-GWs in a pool. A DeNBsupporting the mobile relay node can be connected to multiple MMEs. Ifthe mobile relay node attaches to the DeNB, the DeNB needs to beconnected to the MME which supports the mobile relay node. Accordingly,the DeNB needs to know that the relay node trying to attach to the DeNBis the mobile relay node, and whether the MME supports the mobile relaynode or not.

A handover procedure may be supported in 3GPP LTE-A. Currently, inRRC_CONNECTED state, the network controls the handover procedure per UEbasis. That is, the network decides the movement of each UE toward a newcell. The network triggers the handover procedure based on the radioconditions and load. When the mobile relay node is deployed, it isexpected that handover occurs much more frequently, and the excessivesignaling overhead will be incurred from per UE based handover. Forexample, massive UEs served by the mobile relay node may perform thehandover procedure at the same time toward the same target eNB (or DeNB)when a high speed train having the mobile relay node stops at thestation in the high speed railway scenario. Accordingly, the handoversuccess rate will be reduced due to the excessive signaling overhead andthe fact that tracking area update (TAU) is provided in a short periodof time. Furthermore, UE measurements in high speed environments aretypically less accurate than low speed environments. The UEs on themobile relay node attached to the high speed public transportation willsuffer from the reduced handover success rate. Accordingly, a groupmobility handover procedure can be employed. A handover success rate canbe improved by per group based handover instead of per UE basedhandover. When the mobile relay node tries to handover to the targetDeNB, the target DeNB needs to be connected to the MME which supportsthe mobile relay node. Accordingly, the DeNB needs to know that therelay node trying to handover to the target DeNB is the mobile relaynode, and whether the MME supports the mobile relay node or not.

Therefore, optimization is needed to resolve the problems.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for selecting amobility management entity (MME) in a wireless communication systemincluding a mobile relay node. The present invention provides a methodof receiving an indicator from a mobile relay node and an MME supportingthe mobile relay node.

In an aspect, a method for selecting, by a donor eNodeB (DeNB), amobility management entity (MME) in a wireless communication systemincluding a mobile relay node is provided. The method includes receivinga mobile relay indicator from the mobile relay node during a radioresource control (RRC) connection establishment procedure, receiving amobile relay support indication from an MME supporting the mobile relaynode during an S1 setup procedure between the MME and the DeNB, andselecting the MME supporting the mobile relay node among a plurality ofMMEs.

The mobile relay indicator may indicate the mobile relay node is a relaynode which is mobile.

The mobile relay support indication may indicate whether the MMEsupports the mobile relay node or not.

The method may further include performing an S1 setup procedureinitiated by the mobile relay node.

The method may further include performing an S1 eNB configuration updateprocedure with the MME after performing the S1 setup procedure ifconfiguration data for the DeNB is updated.

The method may further include performing an X2 setup procedureinitiated by the mobile relay node.

The method may further include performing an X2 eNB configuration updateprocedure with neighbor eNBs to update cell information after performingan X2 setup procedure.

In another aspect, a donor eNodeB (DeNB) for selecting a mobilitymanagement entity (MME) in a wireless communication system including amobile relay node is provided. The DeNB includes a radio frequency (RF)unit configured for transmitting or receiving a radio signal, and aprocessor, operatively coupled to the RF unit, and configured forreceiving a mobile relay indicator from the mobile relay node during aradio resource control (RRC) connection establishment procedure,receiving a mobile relay support indication from a mobility managemententity (MME) supporting the mobile relay node during an S1 setupprocedure between the MME and the DeNB, and selecting the MME supportingthe mobile relay node among a plurality of MMEs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS).

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 4 shows an example of structure of a physical channel.

FIG. 5 shows a block diagram illustrating network structure of an LTE-Asystem introducing a relay system.

FIG. 6 shows a basic intra-mobile management entity (MME)/servinggateway (S-GW) handover procedure.

FIG. 7 shows a simplified handover procedure supporting a groupmobility.

FIG. 8 shows the proposed method according to an embodiment of thepresent invention.

FIG. 9 shows the proposed method according to another embodiment of thepresent invention.

FIG. 10 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 6 shows a basic intra-mobile management entity (MME)/servinggateway (S-GW) handover procedure.

In E-UTRAN, network-controlled UE-assisted handovers may be performed inRRC-CONNECTED state. Part of the handover command comes from the targeteNB and is transparently forwarded to the UE by the source eNB. Toprepare the handover procedure, the source eNB passes all necessaryinformation to the target eNB (e.g. E-RAB attributes and RRC context).When a carrier aggregation (CA) is configured and to enable secondaycell (SCell) selection in the target eNB, the source eNB can provide indecreasing order of radio quality a list of the best cells. Both thesource eNB and the UE keep some context (e.g. C-RNTI) to enable thereturn of the UE in case of handover procedure failure. The UE accessesthe target cell via a random access channel (RACH) following acontention-free procedure using a dedicated RACH preamble or following acontention-based procedure if dedicated RACH preambles are notavailable. If the RACH procedure towards the target cell is notsuccessful within a certain time, the UE initiates radio link failurerecovery using the best cell.

The preparation and execution phase of the handover procedure isperformed without evolved packet core (EPC) involvement. It means thatpreparation messages are directly exchanged between the eNBs. Therelease of the resources at the source side during the handovercompletion phase is triggered by the eNB. In case an RN is involved, itsDeNB relays the appropriate S1 messages between the RN and the MME(S1-based handover) and X2 messages between the RN and target eNB(X2-based handover). The DeNB is explicitly aware of a UE attached tothe RN due to the S1 proxy and X2 proxy functionality.

First, the handover preparation procedure is described.

0. Area restriction information is provided. The UE context within thesource eNB contains information regarding roaming restrictions whichwhere provided either at connection establishment or at the last timingadvance (TA) update.

1. The source eNB configures the UE measurement procedures according tothe area restriction information, and transmits a measurement controlmessage to the UE through L3 signaling. Measurements provided by thesource eNB may assist the function controlling the UE's connectionmobility. Meanwhile, the packet data is exchanged between the UE and thesource eNB, or between the source eNB and the serving gateway.

2. The UE transmits measurement reports by the rules set by i.e. systeminformation, specification etc to the source eNB through L3 signaling.

3. The source eNB makes handover decision based on the measurementreports and radio resource management (RRM) information.

4. The source eNB transmits a handover request message through L3signaling to the target eNB passing necessary information to prepare thehandover procedure at the target side. UE X2/UE S1 signaling referencesenable the target eNB to address the source eNB and the EPC. The evolvedradio access bearer (E-RAB) context includes necessary radio networklayer (RNL) and transport network layer (TNL) addressing information,and quality of service (QoS) profiles of the E-RABs.

In the case of a UE under an RN performing handover procedure, thehandover request message is received by the DeNB, which reads the targetcell ID from the message, finds the target eNB corresponding to thetarget cell ID, and forwards the X2 message toward the target eNB.

In the case of a UE performing handover procedure toward an RN, thehandover request is received by the DeNB, which reads the target cell IDfrom the message, finds the target RN corresponding to the target cellID, and forwards the X2 message toward the target RN.

5. The target eNB performs admission control. The admission control maybe performed dependent on the received E-RAB QoS information to increasethe likelihood of a successful handover, if the resources can be grantedby target eNB. The target eNB configures the required resourcesaccording to the received E-RAB QoS information and reserves a C-RNTIand optionally a RACH preamble. The AS-configuration to be used in thetarget cell can either be specified independently (i.e. an“establishment”) or as a delta compared to the AS-configuration used inthe source cell (i.e. a “reconfiguration”).

6. The target eNB transmits a handover request acknowledge message tothe source eNB through L3 signaling, and prepares the handover. Thehandover request acknowledge message may include a transparent containerto be sent to the UE as an RRC message to perform the handover. Thetransparent container may include a new C-RNTI, target eNB securityalgorithm identifiers for the selected security algorithms, a dedicatedRACH preamble, and possibly some other parameters i.e. accessparameters, SIBs, etc. The handover request acknowledge message may alsoinclude RNL/TNL information for the forwarding tunnels, if necessary.Meanwhile, as soon as the source eNB receives the handover requestacknowledge message, or as soon as the transmission of the handovercommand is initiated in the downlink, data forwarding may be initiated.

7. The target eNB transmits an RRC connection reconfiguration messageincluding mobility control information to perform the handover, to besent by the source eNB to the UE. The source eNB performs the necessaryintegrity protection and ciphering of the message. The UE receives theRRC connection reconfiguration message with necessary parameters. The UEis commanded by the source eNB to perform the handover procedure. The UEdoes not need to delay the handover execution for delivering the hybridautomatic repeat request (HARQ)/automatic repeat request (ARQ) responsesto the source eNB.

Hereafter, the handover execution procedure will be described.

The UE detaches from old cell and synchronizes to new cell. In addition,the source eNB delivers buffered and in-transit packets to the targeteNB.

8. The source eNB transmits a serial number (SN) status transfer messageto the target eNB to convey the uplink packet data convergence protocol(PDCP) SN receiver status and the downlink PDCP SN transmitter status ofE-RABs for which PDCP status preservation applies. The uplink PDCP SNreceiver status may include at least the PDCP SN of the first missing ULSDU and a bit map of the receive status of the out of sequence UL SDUsthat the UE needs to retransmit in the target cell, if there are anysuch SDUs. The downlink PDCP SN transmitter status indicates the nextPDCP SN that the target eNB shall assign to new SDUs, not having a PDCPSN yet. The source eNB may omit sending this message if none of theE-RABs of the UE shall be treated with PDCP status preservation.

9. After receiving the RRC connection reconfiguration message includingthe mobility control information, the UE performs synchronization to thetarget eNB and access the target cell via RACH. The access to the targetcell via the RACH may be a contention-free procedure if a dedicated RACHpreamble was indicated in the mobility control information. Or, theaccess to the target cell via RACH may be a contention-based procedureif no dedicated preamble was indicated. The UE derives target eNBspecific keys and configures the selected security algorithms to be usedin the target cell.

10. The target eNB responds to the synchronization of the UE with ULallocation and timing advance.

11. When the UE has successfully accessed the target cell, the UEtransmits an RRC connection reconfiguration complete message (C-RNTI) toconfirm the handover procedure, along with an uplink buffer statusreport, whenever possible, to the target eNB to indicate that thehandover procedure is completed for the UE. The target eNB verifies theC-RNTI sent in the RRC connection reconfiguration complete message. Thetarget eNB can now begin transmitting data to the UE. The packet data isexchanged between the UE and the target eNB.

Hereafter, the handover completion procedure will be described.

12. The target eNB transmits a path switch request message to MME toinform that the UE has changed cell.

13. The MME transmits a user plane update request message to a servinggateway (S-GW).

14. The S-GW switches the downlink data path to the target side. TheS-GW transmits one or more end marker packets on the old path to thesource eNB and then can release any U-plane/TNL resources towards thesource eNB.

15. The S-GW transmits a user plane update response message to MME.

16. The MME transmits a path switch acknowledge message to the targeteNB to confirm the path switch request message.

17. The target eNB transmits a UE context release message to the sourceeNB to inform success of the handover procedure and trigger the releaseof resources by the source eNB.

18. When the UE context release message is received, the source eNB canrelease radio and C-plane related resources associated to the UEcontext. Any ongoing data forwarding may continue.

FIG. 7 shows a simplified handover procedure supporting a groupmobility.

The method described in FIG. 7 may be applied when a high speed trainstops at a station in a high speed public transportation scenario. TheUEs try to handover to the target eNB. The mobile relay forwards ahandover request message containing the list of UEs toward the targeteNB when it receives the measurement reports from a group ofcorresponding UEs. That is, during each predefined (subsequent) timeperiod, the handover requests from multiple UEs are grouped into asingle handover request for the same target eNB and the grouped handoverrequests are sent to the respective target eNBs on the time periodbasis. The number of the grouped handover request may be at least one.That is, a plurality of UEs may be grouped into a single group or aplurality of groups. When a target eNB receives the handover requestmessage, it performs the admission control for the UEs. The target eNBthen returns a handover request acknowledge message containing the listof admitted UEs for handover. If the plurality of UEs is grouped intothe plurality of groups, the handover request acknowledge message maycontain the list of admitted UEs for each group.

0. Area restriction information is provided. The UE context within thesource eNB contains information regarding roaming restrictions whichwhere provided either at connection establishment or at the last timingadvance (TA) update.

1. The mobile relay node configures the UE measurement procedures, andtransmits a measurement control message to the UEs through L3 signaling.Measurements provided by the mobile relay node may assist the functioncontrolling the UE's connection mobility.

2. The UEs transmit measurement reports to the mobile relay node throughL3 signaling.

3. The mobile relay node makes handover decision based on RRMinformation.

4. The mobile relay node transmits a handover request message to thetarget eNB through L3 signaling to prepare the handover procedure at thetarget eNB.

When the mobile relay node receives multiple measurements reports fromthe UEs, the mobile relay node transmits the handover request messagecontaining information on a list of UEs toward the target eNB. Asexplained before, the handover request message contains the informationfor multiple UEs for the same target eNB. Also, the grouping of handoverrequests (e.g., via measurement reports) from multiple UEs into a singlehandover request message may be done in a predefined time period basis.That is, during each predefined time period, the handover requests frommultiple UEs may be grouped into the single handover request messagewhich contains the information on the corresponding UEs. So, the groupedhandover request message is transmitted to the same target eNB on apredefined time period basis.

5. After receiving the handover request message from the mobile relaynode, the target eNB performs admission control for the UEs contained inthe list of UEs in the handover request message.

The admission control may be performed dependent on the received E-RABQoS information to increase the likelihood of a successful handover, ifthe resources can be granted by target eNB. The target eNB configuresthe required resources according to the received E-RAB QoS informationand reserves a C-RNTI and optionally a RACH preamble.

6. The target eNB returns a handover request acknowledge message as aresponse to the handover request message towards the mobile relay nodethrough L3 signaling, and prepares the handover.

When the mobile relay node is employed, an S1-flex problem can beoccurred. A DeNB supporting the mobile relay node can be connected tomultiple MMEs. If the mobile relay node attaches to the DeNB, the DeNBneeds to be connected to the MME which supports the mobile relay node.However, the DeNB does not know that the relay node trying to attach tothe DeNB is the mobile relay node, and whether the MME supports themobile relay node or not. A handover problem can also be occurred. Whenthe mobile relay node tries to handover to the target DeNB, the targetDeNB needs to be connected to the MME which supports the mobile relaynode. However, the DeNB does not know that the relay node trying tohandover to the target DeNB is the mobile relay node, and whether theMME supports the mobile relay node or not. Considering the NAS nodeselection function of relay node is controlled by the DeNB, it isimportant to notify the DeNB that it is a mobile relay node, based onwhich the DeNB can select the MME which supports the group mobility whenit takes the responsibility of NAS node selection.

FIG. 8 shows the proposed method according to an embodiment of thepresent invention.

In step S200, the relay node attach procedure is performed. In the relaynode attach procedure, an RRC connection setup is performed between themobile relay node and the DeNB. At this time, the mobile relay nodetransmits a mobile relay node indicator to the DeNB during the RRCconnection establishment. The mobile relay node indicator indicates thatwhether the relay node is a mobile relay node or not. Also, an S1 setupis performed between the DeNB and the MME supporting the mobile relaynode. At this time, the MME supporting the mobile relay node transmits amobile relay node support indication to the DeNB during the S1 setup.The mobile relay node support indication indicates whether the MMEsupports the mobile relay node or not.

In step S201, an OAM completes the relay node configuration

After the DeNB initiates setup of bearer for S1/X2, the mobile relaynode initiates the setup of S1 and X2 associations with the DeNB. Instep S220, the mobile relay node initiates the S1 setup. In step S230,the mobile relay node initiates the X2 setup. In addition, the DeNB mayinitiate an RN reconfiguration procedure via RRC signalling forRN-specific parameters.

After the S1 setup, the DeNB performs the S1 eNB configuration updateprocedure in step S221, if the configuration data for the DeNB isupdated due to the relay node attach procedure. After the X2 setup, theDeNB performs the X2 eNB configuration update procedure to update thecell information in step S231.

FIG. 9 shows the proposed method according to another embodiment of thepresent invention.

In step S300, the DeNB receives a mobile relay node indicator from themobile relay node during the RRC connection establishment in the relaynode attach procedure. The mobile relay node indicator indicates thatwhether the relay node is a mobile relay node or not. In step S310, theDeNB receives a mobile relay node support indication from the MMEsupporting the mobile relay node during the S1 setup between the MME andthe DeNB in the relay node attach procedure. The mobile relay nodesupport indication indicates whether the MME supports the mobile relaynode or not. In step S320, the DeNB selects the proper MME whichsupports group mobility for the mobile relay node among a plurality ofMMEs.

By receiving the indicator from the mobile relay node and the MMEsupporting the mobile relay node, the DeNB can solve the S1-flexproblem, the handover problem, and other problems related to the mobilerelay node.

FIG. 10 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A DeNB 800 includes a processor 810, a memory 820, and a radio frequency(RF) unit 830. The processor 810 may be configured to implement proposedfunctions, procedures, and/or methods in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The RF unit 830 isoperatively coupled with the processor 810, and transmits and/orreceives a radio signal.

A mobile relay node or an MME supporting the mobile relay node 900 mayinclude a processor 910, a memory 920 and a RF unit 930. The processor910 may be configured to implement proposed functions, procedures and/ormethods described in this description. Layers of the radio interfaceprotocol may be implemented in the processor 910. The memory 920 isoperatively coupled with the processor 910 and stores a variety ofinformation to operate the processor 910. The RF unit 930 is operativelycoupled with the processor 910, and transmits and/or receives a radiosignal.

The processor 910 may include an application-specific integrated circuit(ASIC), another chip set, a logical circuit, and/or a data processingunit. The RF unit 920 may include a baseband circuit for processingradio signals. In software implemented, the aforementioned methods canbe implemented with a module (i.e., process, function, etc.) forperforming the aforementioned functions. The module may be performed bythe processor 910.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

1. A method for selecting, by a donor eNodeB (DeNB), a mobilitymanagement entity (MME) in a wireless communication system including amobile relay node, the method comprising: receiving a mobile relayindicator from the mobile relay node during a radio resource control(RRC) connection establishment procedure; receiving a mobile relaysupport indication from an MME supporting the mobile relay node duringan S1 setup procedure between the MME and the DeNB; and selecting theMME supporting the mobile relay node among a plurality of MMEs.
 2. Themethod of claim 1, wherein the mobile relay indicator indicates themobile relay node is a relay node which is mobile.
 3. The method ofclaim 1, wherein the mobile relay support indication indicates whetherthe MME supports the mobile relay node or not.
 4. The method of claim 1,further comprising performing an S1 setup procedure initiated by themobile relay node.
 5. The method of claim 4, further comprisingperforming an S1 eNB configuration update procedure with the MME afterperforming the S1 setup procedure if configuration data for the DeNB isupdated.
 6. The method of claim 1, further comprising performing an X2setup procedure initiated by the mobile relay node.
 7. The method ofclaim 6, further comprising performing an X2 eNB configuration updateprocedure with neighbor eNBs to update cell information after performingan X2 setup procedure.
 8. A donor eNodeB (DeNB) for selecting a mobilitymanagement entity (MME) in a wireless communication system including amobile relay node, the DeNB comprising: a radio frequency (RF) unitconfigured for transmitting or receiving a radio signal; and aprocessor, operatively coupled to the RF unit, and configured for:receiving a mobile relay indicator from the mobile relay node during aradio resource control (RRC) connection establishment procedure;receiving a mobile relay support indication from a mobility managemententity (MME) supporting the mobile relay node during an S1 setupprocedure between the MME and the DeNB; and selecting the MME supportingthe mobile relay node among a plurality of MMEs.
 9. The DeNB of claim 8,wherein the mobile relay indicator indicates the mobile relay node is arelay node which is mobile.
 10. The DeNB of claim 8, wherein the mobilerelay support indication indicates whether the MME supports the mobilerelay node or not.
 11. The DeNB of claim 8, wherein the processor isfurther configured for performing an S1 setup procedure initiated by themobile relay node.
 12. The DeNB of claim 11, wherein the processor isfurther configured for performing an S1 eNB configuration updateprocedure with the MME after performing the S1 setup procedure ifconfiguration data for the DeNB is updated.
 13. The DeNB of claim 8,wherein the processor is further configured for performing an X2 setupprocedure initiated by the mobile relay node.
 14. The DeNB of claim 13,wherein the processor is further configured for performing an X2 eNBconfiguration update procedure with neighbor eNBs to update cellinformation after performing an X2 setup procedure.